Grinding-mill



(No Model.) G. PORSTER.

GRINDING MILL,

Patented Dec. 6,1881.

MIT'IESSES UNITED STATES PATENT OFFICE.

CHARLES FORSTER, OF PITTSBURG, PENNSYLVANIA.

GRINDING-MILL.

SPECIFICATION forming part of Letters Patent No. 250,432, dated December6, 1881-,

' Application filed September 21, 1881.. (No model.) 7 i To all whom itmay concern:

4 Be it known that I, CHARLES FORSTER, of Pittsburg, in the county ofAllegheny and State of Pennsylvania, have invented a new and usefulImprovement in Grinding-Mills; and I do hereby declare the following tobe a full, clear, and exact description thereof.

My invention relates to an improvement in grinding-mills for grindinglime, quartz, chalk, and like substances; and it consists of a millhaving an inner cone over which is an outer shell, the grinding-surfacesof which are provided with grooves extending spirally downward andgradually decreasing in depth from the top and increasing in width towithin a short distance of the base. Between these grooves are ridges orlands having a flat surface. At the base of the shell and cone thesurfaces are quite smooth and touch each other. At or about the pointwhere the grooves end the surfaces separate from each other at an .acuteangle upward, so as to gradually increase the distance apart between theshell and the cone.

Heretofore grindingmills for lime, chalk, &c., have been provided withgrooves or teeth extending to a point near the base of the cone andshell. From this point to the base the surfaces were provided withdiamond-shaped teeth, which served to pulverize and deliver thesubstance ground. When, however, these teeth became worn the mill wouldnot deliver the ground lime and became useless. In my mill the crushedlime or other substance is carried down the spiral grooves, is forcedbetween the smooth surfaces at the base, and is thence delivered in apulverized condition.

I will now describe my invention, so that others skilled in the art maymanufacture and use the same, reference being had to the accompanyingdrawings, in which-- Figure 1 is a sectional view, showing the shell andgrinding-cone of my improved mill. Fig. 2 is a sectional view of theshell. Fig. 3 is an elevation of the grinding-cone.

Like letters of reference indicate like parts in each.

In the drawings, a represents the outer shell, the lower portion ofwhich is shaped in the form of a frustum of a cone, at the top of whichthe shell widens, so as to form per a. From the point a of the shellgrooves a extend spirally down along the surface to the point a. Fromthe point a to the base of the shell the surface is perfectly smooth.Inside of the shell a is a grinding-cone, b, upon the surface of whichare grooves 1), similar to the grooves a on the surface of the shell a,excepting that they extend spirally downward in the opposite directionto the grooves on the shell. From the point where the grooves end on thecone 1) to the base of the cone is a smooth surface, I). The surface ofthe lands or spaces between the grooves is smooth. From the upperportion of the cone 1) extends a cylinder, 0, to a point on a level withthe top of the hopper a. The grooves b, which extend down the cone 1),start from the top of this cylinder, which may be formed in one piecewith the cone. The cone 1) is suitably mounted, so as to turn in theshell a, the plain surfaces of the shell and cone at their base touchingeach other. From this point, however, the grinding-surfaces of the coneand shell separate from each other at an acute angle,-increasing thedistance apart to the point where the hopper'of the shell flaresoutward.

The operation is as follows: The lime, chalk, or other substance to beground is placed in the hopper of the mill, the cone revolving. The limeor other substance is broken by the spaces between the grooves, and iscarried down the grooves and is delivered between the smooth surfaces atthe base of the mill in a finely-ground condition, where itis'pulverized and discharged from the mill.

The advantages of my invention are that the lime, 850., is morethoroughly ground than could be done with the mills now in use, and mymill will last much longer than other mills,'as it has the hopon theinner surface no teeth to become dull and wear away, therev bydecreasing the efficiency of the mill until it becomes worthless.

Having thus described my invent-ion, what I claim, and desire to secureby Letters Patent, is-

1. The combination, in a grinding-mill, of an outer shell and an innercone, the grindingsnrfaces of which are provided with grooves extendingspirally to a point near the base of the same, the grooves on the coneextending in an opposite direction to the grooves on the shell, andarranged so as to leave lands or spaces having a smooth surface situatedbetween said grooves, the lower portion of the grinding-surfaces of thecone and shell being smooth, substantially as and for the purposespecified.

2. The combination, in a grinding-mill, of an outer shell and an innercone, the grindingsurfaces of which are provided with grooves extendingspirally to a point near the base of the same, the grooves on the coneextending in an opposite direction to the grooves on the shell, saidgrooves being arranged to leave lands or spaces having a smooth surfacesituated between said grooves, the lower portion of thegrinding-surfaces of the cone and shell being smooth, and thegrinding-surfaces of the cone and shell separating from each other at anacute angle from the bottom of the grooves, substantially as and for thepurposes described. 3. In a grinding-mill, the combination of the outershell, the upper portion of which is formed in the shape of a hopper,and a portion of the inner surface of the shell being provided withgrooves extending spirally thereon, and an inner cone, from the upperportion of which a cylinder extends to the top of the hopper, thesurface of the cylinder and a portion of the surface of the cone beingprovided with spiral grooves, the lower portion of the grinding-surfacesof the shell and cone being smooth, substantially as and for thepurposes specified.

- In testimony whereof I have hereunto set my hand. 7

CHARLES FORSTER. Witnesses:

JAMES K. BAKEWELL, L. O. FITLER.

